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Thursday August 24, 2017 - The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory

By John Ensworth Discussion: A progressive weather pattern continues which means troughs and ridges are on the move across the U.S.
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This content was originally published by the Longmont Observer and is licensed under a Creative Commons license.

By John Ensworth

Discussion:

A progressive weather pattern continues which means troughs and ridges are on the move across the U.S.  We have a ridge running over us over today which would mean low to mid 90’sF, but, as Figure 1 shows, there is a good amount of moisture flowing up into the core of the ridge from the tropics and desert southwest (monsoon-like). Figure 2 also shows this moisture source riding in.  So the highs today will be cut off in the 80’s.  We might touch 90F on Friday with the moisture axis following the progression of upper air troughs and ridges, but while the ridge is still relatively nearby.  The stable air east of the Rockies is warming up and moistening up making things more unstable. Daily thunderstorms firing in the mountains should make it onto the Plains today and become sever. Figure 3 shows the Marginal Risk (1 on a scale of 1-5) of severe weather just east of I-25 today. The primary threat is for large hail and strong winds.  Since this was issued Wednesday PM, a fresh look at the data this morning might move that risk back to include Longmont.

Figure 1:  The Wednesday PM 500mb map from the RAP analysis.  Moisture flow into the ridge is shown in green.

Figure 2:  The water vapor satellite from Wednesday PM.

Figure 3: The Storm Prediction Center severe weather outlook Day 2 for Thursday issued Wednesday PM.

In a look at the longer range:

By tonight, the stalled front out east, upslope surface moisture and midlevel tropical moisture will help kick of more rain (and thunderstorm) chances (Figure 4). Things dry out after that into the weekend as a ridge builds in.  You can see the big ridge west of us by Monday night giving us northeasterly flow – that will be cooler and moister air on the way in.  Tropical System Harvey will come ashore soon in Texas and sit there up against the front giving days of rain to SE Texas (Figure 5).

Figure 4: The NCEP forecasted surface analysis with future rain chances covering Thursday PM.

Figure 5: The GFS forecasted upper air pattern for Tuesday Morning.

As a bonus, I have an automated weather station at Cherrywood Observatory and you can see the drop in relatvie sky temperature (top chart), the drop in air temperature (middle chart) and rise in relative humidity (lower right chart) during the partial eclipse in Longmont.  RH rises since it is dependent on both the amount of moisture (unchanged) and the temperature of the water vapor (it dropped with the air temperature).  Fun!

*** This feature will run as close to daily as possible in this location on the Longmont Observer. ***

This article will provide a brief discussion concerning the ‘why’ behind the weather with a focus on severe weather, unusual weather, and snow (especially trying to predict snow depth and its human impact in Longmont).

Bio:

John Ensworth works from Longmont as the Principle Investigator for the NASA Science Mission Directorate Earth and space science education product review through the IGES (The Institute for Global Environmental Strategies – www.strategies.org) .  He is in his 14th year running this review.  He is an astronomer (from the 2nd grade onward) and became a meteorologist (in the 5th grade) when a thunderstorm in Arizona rained on his telescope when the weather service had only forecasted a 10% chance of rain.  He has college degrees in physics and astronomy and climatology and a graduate degree in meteorology and earth science.  He lectures at the Little Thompson Observatory in Berthoud, the Estes Park Memorial Observatory in Estes Park, and for a number of online universities. He built and runs a backyard observatory near Pace and 17th in northeast Longmont where he has lived for 8 years with his wife, daughter, son, and two cats. Invitations to open house nights at this observatory, LTO, and EPMO will be posted with future discussions when they are scheduled.

Forecasting severe weather and snow amounts via text lead to this column.  He began texting friends about the weather right after the September 2013 flood.  The readers of this column will, hopefully, keep him honest in what he ‘thought’ he had forecasted for ‘the most recent’ storm.